1. Field of the Invention
This invention relates to a plastic snap hinge closure having a lower part and an upper part connected with it by means of a film hinge, where the closure shell walls in the area of the film hinge are either straight or curved and have at least one tension element connected with both closure parts, preferably in one injection-molded piece, and each tension element is either directly or indirectly connected to the shell walls of both closure parts.
2. Description of the Prior Art
Conventional plastic snap hinge closures are known, for example, from my European Patent Disclosures Nos. 0 147 423 and 0 291 457. In the first mentioned patent disclosure, the tension elements are tension straps, which are produced by means of injection molding over consoles on the shell wall of the lower part and of the lid and thus are located in one plane. In the second mentioned patent disclosure, the tension straps are disposed extending approximately in or on the shell wall.
In the first mentioned example, the tension straps extend in one plane in the closed position and the attachment points of the tension straps are displaced out of the shell wall by consoles in such a way that they are located parallel to the main axis. In the second mentioned example, the tension straps extend in two planes which between them enclose an angle. Accordingly, the outer sections of each of the tension straps must travel a greater distance during opening than the inner sections of the straps located more closely to the hinge.
According to Wiesinger, European Patent Disclosure No. 0 056 469, instead of tension straps triangular intermediate elements, which verge with their tips into the main hinge, are disclosed.
Regarding an explanation of the operation of various conventional snap hinge closures, tension straps taught by the two first mentioned patent disclosures are supposed to elastically stretch and thus provide a snap effect. In practice, however, plastic materials used for plastic closures hardly have the ability of stretching elastically. This means that the desired snap effect cannot actually be achieved.
The function in connection with another embodiment taught by European Patent Disclosure No. 0 056 469 is correctly explained. The action of the snap closure is based on the elastic deformation of the closure in the area of the hinge. This means that in the course of each opening or closing of the closure, the shell wall of the lower part or the lid, or of the entire lid, arches in the area of the passage across the dead center position in the course of operation and subsequently is bent back into the relaxed, non-deformed shape.
Of course, this is an undesirable cooperation of forces which are hard to predict and interact in a complex manner. Attainment of the snap action can only be determined empirically and is difficult to predict. Easier to predict are results in connection with snap closures operating with a toggle joint, one of the levers of which extends into the surface of the lid and the other into the shell wall of the lid and the lower part. With these conventional closures, the snap effect depends on the force required to deform the two levers of the toggle joint. However, a hinge of this type is only suitable for closures having a small spout, where the lid itself does not close off the spout, but a sealing element placed thereon and cooperating with the spout closes off the spout, since the lid itself cannot seal because of the cuts along the toggle joint.
Accordingly it is desired to provide snap hinge closures, the snap effect of which does not depend on the elastic action of some arbitrary part of the closure, except for the tension element.